As well known, such compression units may be variously used, such as in refrigerating systems.
It is known that rotary compressors and particularly screw rotary compressors require a continuous injection of lubricating oil which, in addition to lubrication, also performs the function of subtracting part of the heat developed by compression work to maintain the operating temperature within reasonable limits. In turn, said oil has to be cooled down.
As well known, such units would comprise a separator, that is an apparatus supplied with the mixture of compressed gas and oil from the compressor; in said apparatus oil is separated from gas and the latter is then supplied to a condenser and therefrom to use, while oil is sent to the compressor by a pump.
Thus, in such a known type of unit, a chiller or cooler is provided dowstream of the separator on the line for oil return to the compressor, that is an apparatus suitably designed for oil cooling, so that oil returns to the compressor at cooled state. However, while achieving the object of sufficient oil cooling, said system has the disadvantage of being quite costly because of requiring a suitable apparatus, that is the above mentioned chiller or cooler. A cooling system has also been proposed which provides the use of a portion of the chilled liquid from said condenser and directed to the user. According to said system, some portion of liquid refrigerating fluid is injected in the compressor during compression step at a location where an intermediate pressure exists between suction pressure and exhaust pressure. However, by such a system the compressor performances are impaired.